Question

1. The feedback is negative. True or False?

Rs X In the above figure, all amplifiers are voltage amplifiers with A1 = 20, A2 = -1, A3 = +2 Answer the following questions considering the amplifiers have infinite input and zero output impedances:

2. Find the value of the forward amplifier gain

3. If R1=10kΩ, what value should R2 have to have a feedback factor of 1/2?

4. The closed-loop gain is about …

(Hint: The closed-loop gain is positive)

A) 1.5

B) 2.8

C) 1.9

D) 3.7

5) If the overall forward amplifier has a 150 Hz bandwidth (due to a single dominant pole), the bandwidth of the closed-loop circuit would be around …

A) 1840 Hz

B) 2100 Hz

C) 3150 Hz

D) 2650 Hz

From this point on consider that the first amplifier has an input impedance of 2kΩ and the third amplifier has an output impedance of 10kΩ:

6. The circuit closed-loop input impedance would be about ... kΩ

a) 42

b) 24

c) 30

d) 35

7.

The circuit closed-loop output impedance would be about … kΩ

a) 0.68

b) 0.82

c) 0.48

d) 0.57

8.

If RS=1kΩ and RL=10kΩ, the approximate value of _{$\frac{Y}{V_S}$} would be …

a) 2.2

b) 1.8

c) 3.3

d) 2.6

Answer 1

Gain is directly Multiplied.

© It is negative feedback h as a part of output is getting subtracted from input -ora Output increase will decrease the input which decrease the output - so negative feedback. - B value of forword Amplifier gain A = A, XA2 X A3 - Just Multiply the Grain A = 20% (-1) * (2) = 40. 0 feedback factor will be 1 - R2 = RitR2 2 R2= lok+R 2 R2=lokal

① Close loop gain Aon (- Vs + 1 2 2 ) Pory ADLEV) = yli - AOL it om = 109 ©

5 BW Openloop = 150 HZ GaintBw = Constant loop Grain. 1So x — Чо - AcxBubc - Close 150 x 40 =BW close loop log 3157-89 Hz=BW [BW ~ 3150 Hz)

1. Sompling Input is not directly connected to feed back compo nout so Current input impedence = RiXD (Desenstivity) = 2 x 21=42k ? D = 1- BA D=1-41-40) = 21

0 Output Node is directly connected to feedback component so. bos Voltage sampling Ow put impedence = Ro = 10kr 1 Desensitivity D 2 0.476kRn 0.48K2 @ Rs=1ks 2K w 0.48k AGLV lok} Re Yess vs 0 42K & v Close loop gain. Voltage divider. V = VSX42K = (42+)K ACL V X loka TO+0.48)* Y = 109x42 x 10 ū3 10:48 - 1077 108